The photographic quality of silver halide photographic light-sensitive materials is evaluated based on gradation, sensitivity and fog. Stimulated by the recent trend in the photographic art for increased sensitivity, excellent gradation and sensitivity with low fog have been demanded. Therefore, the development of technique that meets the strong demand for all of the high sensitivity, low fog, and harder gradation or high contrast is strongly needed.
To meet the need above, several methods have been developed in order to obtain photographic light-sensitive materials having high sensitivity and higher contrast as well as low fog. The methods usually used in the art to attain high sensitivity include those, for example, disclosed in British Pat. No. 1,315,755, Japanese Patent Examined Publication No. 15748/1969, U.S. Pat. Nos. 2,410,689, 2,983,610, 3,297,446, 3,441,914, 3,591,384, 3,761,267, 3,901,714, 4,054,457, 4,067,740, Research Disclosure Nos. 12008, 13452, and 13654; and "The Theory of the Photographic Process" (4th Ed., Nacoillan, 1977), pp.67-76. However, these methods often provides dilemma; improving sensitivity often incurs greater fog, or lower contrast.
With respect to production of contrasty gradation in picture images research work by the photographic material industry is being devoted to designing silver halide photographic sensitive materials which have desirable gradation characteristics adapted to the specific uses. The gradation property can be broadly divided into the gradation in the range from high density to medium density hereinafter referred to as "shoulder gradation", and that in the range from medium density to low density, hereinafter referred to as "toe gradation", which both are an important property bearing significantly upon the picture images in vividness and sharpness produced in silver halide photographic sensitive materials.
One widely known technique for controlling the gradation and keeping it from decreasing of contrast is to change the quantity of the coated silver. This is the most easiest method for the purpose, but usually, this technique applies only to slight adjustments or the like because of the defect that the maximum density is affected, and, moreover, the technique has little effect for controlling the toe gradation.
Another technique familiarized to the photographic material industry is a method in which silver halide emulsions in a plurality of kinds which have the same color-sensitivity but varient sensitivities and have a more contrasty gradation characteristic than is required are contained in one and the same emulsion layer or separately in a plurality of emulsion layers with the same color-sensitivity.
Although this method prevents the contrast from decreasing, yet it is impossible for the method to make the resultant gradation more contrasty than that of said silver halide emulsions of a plurality of kinds used in a mixture and still more so to make the toe gradation of a silver halide emulsion contrasty.
The conventional methods for attaining higher contrast in order to obtain preferred photographic light-sensitive materials include a method of introducing rhodium into silver halide grains, as a doping agent; a method utilizing lith development, wherein hydroquinone is used as a developing agent and a developer having low concentration of sulfite ion is used in treatment; a method using tetrazolium salt, for example, Japanese Patent Publication Open to Public Inspection, hereinafter referred to as Japanese Patent O.P.I. Publication, No. 140340/1987; and a method using hydrazine derivatives for example, Japanese Patent O.P.I. Publication No. 223774/1986.
However, these methods entail drawbacks such as significant desensitization, greater fog, and deteriorated storage stability, and, at the same time, require a special processing solution in the treatment processes.
Particularly, when color photographic light-sensitive materials are treated with these methods, higher contrast is not satisfactorily attained.
A method less susceptible to photographic property deterioration and being readily practicable is a method that increase the coating weights of silver halide and couplers. However, requiring an increased amount of silver, this method disadvantageously incurs increase in cost and the application thereof has been limited to a specific field. A method using a monodispersed emulsion disclosed in Japanese Patent O.P.I. Publication No. 243454/1986 is a method effective in attaining higher contrast. However, this method attains higher contrast often at the cost of tone reproduction because of the balance needed to be coordinated with other photographic properties. Therefore, the method is still unsatisfactory, neccesitating additional means for higher contrast.
To satisfy three photographic criteria i.e. higher sensitivity, smaller fog, and higher contrast, methods for performing chemical sensitization in the presence of tetrazaindene compound were disclosed in Japanese Patent O.P.I. Publication Nos. 126526/1983, and 237545/1985. However, the effects of these methods are still unsatisfactory, and, furthermore, virtually ineffective for high chloride emulsions having high content of silver chloride.
On the other hand, properties of the silver halide photographic material are varied with exposure condition made on which namely sensitivity or contrast of the photographic material is decreased when the material is exposed for long duration with low intensity light or for short duration with high intensity light. Such phenomenon is called as reciprocity failure.
Generally, as explained in "Dictionary of Photographic terms" edited by Photographic Term Committee of Photographic Society of Japan, published by Photo Industry Publishing Company, the term, reciprocity failure means that reciprocity law is not accorded. Phot chemical reaction is ususally progressed in proportion to an irradiated light amount, i.e. the product of a light intensity and an irradiating time, but there may be some instances where the law may not be accorded. The lather is named reciprocity failure. In photosensitive process of silver halide, the reciprocity law is not applicable when the intensity of light is too high or low, and phenomena called high intensity reciprocity failure and low intensity reciprocity failure respectively will often occur.
On the other hand, silver halide light-sensitive materials are required to improve photographic characteristics for adapting various photographing or printing conditions, in particular, the reciprocity failure of photosensitive materials which greatly relate to slope characteristics during printing is one of important characteristics.
As described as slope control in "Dictionary of Photographic Terms" (mentioned above), Page 139, the image density and color balance of a print will be varied when the exposure of the same subject is changed to photograph with a color negative film and the negative is printed by an printer of integral neutral type will be varied. When taking exposure values changed from a proper exposure of the color negative as the abscissa of a graph and taking the reflection density of each color image of the print as the ordinate, the density curves are deviated from a holizontal line. Such deviated curves are called slopes. Generally, the lopes for three colors are different from each other. Changes in printing density and in color balance with respect to the density of the negative film are called slope characteristics. The slope characteristics depend greatly on by the shape of characteristic curve of the negative, the deviation of the average transmitted light of the negative, the performance of the printer, and the reciprocity failure characteristics of photosensitive materials for making prints.
The printer is automatically adjusted to control the slope characteristics. However the adjustment will be insufficient by the cause of some negative film types and the possible degree of overexposure or underexposure. Therefore, techniques for producing photosensitive materials to be easily controlled in its slope for providing prints are called for, that is to say, improved reciprocity failure characteristics are needed. As the method to decrease changes in sensitivity caused from the reciprocity failure by adding an iridium compound to silver halide emulsion, the following are known: a method as described in Japanese Patent Examined Publication No. 4935/1968, a method described in Japanese Patent Examined Publication No. 32738/1970, a method as described in Japanese Patent Publication Open to Public Inspection No. 88340/1977 hereinafter referred to as Japanese Patent O.P.I. Publication, and a method described in Japanese Patent O.P.I. Publication No. 9604/1979.
Though increasing the amount of an iridium compound added for decreasing changes in sensitivity caused from reciprocity failure surely reduces changes in sensitivity, changes in gradation are apt to increase. Actually, the adding amount cannot be increased due to the compromise between sensitivity changes and gradation changes. For multi-layer color photosensitive materials, a blue-sensitive emulsion layer, green-sensitive emulsion layer, and a red-sensitive emulsion layer are generally applied to. Improving the reciprocity failure characteristics with the most required color balance of three layers kept was quite difficult because of the difference of the silver halide emulsion, the sensitizer, optical sensitizing dye, the inhibitor, coupler, and the coating aid of each layer. In particular, it is difficult to reduce changes in the gradation of three the layers and to let the direction of the changes to agree with each other.
For aforementioned reason, if the exposure is constant, a change in the light intensity will give little changes in sensitivity and gradation. In particular, almost no changes in gradation are given.
Therefore, a silver halide photosensitive material with improved reciprocity failure characteristics in called for.
Further, stability of the emulsion is an important factor for manufacturing a high contrast and high sensitive photographic material.
The instability of an emulsion coating poses itself as a problem when, in the fabrication of a silver halide photographic sensitive material, the emulsion coating is applied to the support immediately after the preparation of the coating solution and also after a period of storage, because the deterioration during the storage causes the sensitivity of the silver halide to change and makes it difficult to obtain a photographic sensitive material of uniform quality.
As a means for improving an emulsion coating solution in stability it came into consideration to add to the coating solution of emulsion a compound known as a stabilizer, such as an azole or azaindene, a reducing agent such as hydroquinone or sulfinic acid, or to use a specific copolymer and fluorescent whitening agent in combination as described in Japanese Patent O.P.I. Publication No. 111629/1974. These methods, however, can hardly be considered to satisfactorily improve a coating solution of emulsion in stability during the storage, or some of such compounds may even impair photographic characteristics of vital importance such as gradation or sensitivity.
It is also known to add a sensitizing dye to the coating solution of emulsion for the same purpose, but this method also has a defect in that the sensitizing dye, according as its addition is increased, causes its residual color stains to be increasingly produced.
Now, after exposure a silver halide photographic light-sensitive material is subjected to a processing stage, in which what is commonly termed processing stability is highly required. Therefore, for the purpose of processing such photographic light-sensitive material, an automatic developing machine is generally employed which can produce high quality photographs at low cost and efficently.
In the process of the photographic light-sensitive material being processed by employing such automatic developing machine, a processing solution is subject to decrease in activity with time, and therefore it is customary to replenish the solution by a corresponding amount of such solution, which solution is hereinafter referred to as replenishing solution, to thereby maintain the activity of the processing solution always at constant level, which is hereinafter referred to as continuous replenishment.
Actually, however, even in the case of continuous replenishment, for various reasons there may arise problems, such as changes in the composition and pH of the processing solution, and inclusion of foreign matter, which result in changes in the activity of the processing solution which, in turn, have considerable adverse effect on the photographic performance of the photographic light-sensitive material.
By way of example, continuous replenishment in the case of processing color paper (color photographic paper) in an automatic developing machine is described in further details. After exposure, processing of the color paper in the developing machine is carried out in the following sequence: color development--bleach fix--washing--stabilization. In the automatic developing machine, transport means for color paper, e.g., an endless belt, runs through a color developing bath, a bleach-fixing bath, and a washing or stabilizing bath. Thus, it is likely that a bleach-fix solution deposit on the endless belt will more or less become included in the color developing bath without being fully removed in the stage of washing or stabilizing, which naturally results in varied activity of the color developing solution. Processing with such color developing solution will usually be a cause of a gradation change and/or increased fogging, with the result that the photographic performance of the photographic light-sensitive material is adversely affected.
Therefore, the development of a photographic light-sensitive material which is less liable to changes in its photographic performance characteristics, such as sensitivity, gradation, and fogging, even if there should occur some change in the activity of a processing solution, and which has good processing stability, has been greatly demanded.
Resently, improved hardward such as a printer and automatic developing machine, improved developer solution, improved silver halide color photographic light-sensitive material packaging thereof. As a result, the so-called "mini-laboratory" system, that performs developing of color negative film through preparation of color print even in a limited room for example in one corner of a department store, is increasingly used more commonly.
Under such circumstances, it is a current requirement that a color print of further improved quality be more readily prepared in a shorter period.
Rapid processing of silver halide color photographic light-sensitive materials requires acceleration in each of principal color photographic processes, that is, color developing, bleaching, fixing, washing, and drying. Improvement in color developing, which takes a particularly long period, contributes to overall reduction in processing time.
One of the methods to shorten a color developing time is to use smaller silver halide grains in a light-sensitive material.
This technique, however, inevitably incurs loss in sensitivity. Additionally, the blue-sensitive emulsion layer uses both light absorption by silver halide and light absorption by a sensitizing dye, and, therefore, once a silver halide emulsion of a different grain size is employed, the color balance previously attained by the two types of light absorption will disrupted, and results in another problem in terms of color reproduction. More specifically, the degree of light absorption by silver halide grains is proportional to the third power of grain size, while the degree of light absorption of a sensitizing dye is proportional to the second power of silver halide grain size. Correspondingly, a smaller grain size trends to decrease in sensitivity. At the same time, since the green-sensitive silver halide emulsion is somewhat sensitive to light absorbed with silver halide grains, the green-sensitive emulsion may be developable with blue light. This possibility of accidental development is greater, if the sensitivity of a blue-sensitive emulsion layer becomes lower; an area supposed to be colored in high-density yellow may be stained with magenta color.
Another method for shortening a color developing time is a method that uses development accelerator when an exposed silver halide color photographic light-sensitive material is subjected to developing using an aromatic primary amine color developing agent. The examples of disclosed accelerators include a development accelerator containing quaternary nitrogen atoms; a polyethylene oxide type development accelerator; an imidazole type development accelerator; a polyacrylamido-polyacrylic acid development accelerator; and a development accelerator having a thion group. However, among these development accelerators, those having a relatively higher activity sometimes incur fogging.
Furthermore, a method that incorporates 1-arylpyrazolidone such as 1-aryl-3-pyrazolidone into a silver halide color photographic light-sensitive material that is processed in an extremely short developing time was disclosed.
However, these techniques already disclosed are not necessarily satisfactory in forming a dye image of high density at sufficient high development speed, calling for further improvements.
Japanese Patent O.P.I. Publication No. 50533/1983 discloses a developing promoting method combinedly using 1-aryl-3-pyrazolidone and non-sensitive silver halide grains. This method is also unsatisfactory in promoting development.
Another method is to provide a larger content of silver chloride included in silver halide particles. This method is not satisfactory since the minimum density increases when bleach-fixer is accidentally mixed into a color developer. There has been a defect that only a lowered contrast image may be obtained when development is performed for 60 seconds or less.
Further in such a short time processing as mentioned above, an uneven development occurs around the leading, trailing and side edges of a paper roll or around a hole between picture frames, because the stirring efficiency therearound is different from those in the other areas, thus causing the difference in color balance, and degraded print quality.